The Pacemaker authors transferred the age assignment
of 440 ka for the MIS 12-11 boundary, the age assignment
of 251 ka for the MIS 8-7 boundary, and the age assignment
of 128 ka for the MIS 6-5 boundary to the presumed
corresponding MIS boundaries in the RC11-120 and
E49-18 cores. Technically, however, the Pacemaker authors
did not actually use this last age estimate of 128 ka in
their analysis. Protactinium-thorium dating applied to the
V12-122 Caribbean core had already yielded an age estimate
of 127 ka for the MIS 6-5 boundary, and the Pacemaker
authors felt that this slightly lower age estimate was a little
more accurate.
30 They no doubt, however, considered the
close agreement between these two age estimates of 127 ka
and 128 ka to be a confirmation of the validity of their
assumption of a (nearly) constant sedimentation rate within
the V28-238 core.

They then used these three-age
control (or anchor) points to construct
timescales for the two sediment
cores. For their initial analysis, they
employed simple timescales (which
they dubbed as ‘SIMPLEX’), utilizing
only two age control points within
each core and the assumption of a
constant sedimentation rate. Within
the RC11-120 core, the MIS 6-5
boundary was identified at a depth of
4. 40 m. Hence, an age of 127 ka was
assigned to this depth in the RC11-120
core. An age of 0 ka was assumed for
the top of the RC11-120 core, and ages
were assumed to increase at a constant
rate with depth within the core.

As noted earlier, they completely
excluded the upper third of the E49-18

core from their analysis. The MIS 6-5
boundary was identified at a depth of
4. 90 m within this second core; hence
the age of 127 ka was assigned to this
depth. The MIS 12-11 boundary was
identified at a depth of 14.05 m; hence,
this depth within the E49-18 core was
assigned an age of 440 ka. Again, age
was assumed to increase linearly with
depth down the core.

Spectral analysis

Figure 5 shows the manner in
which three waves of different
frequencies, amplitudes, and phase
constants may be added (superposed) together to yield
a composite waveform. Although the number of waves
needed to construct the δ18O waveforms shown in figures
2 and 3 is much larger, the principle is the same: these
complicated waveforms may also be constructed by adding
together waves of different frequencies, amplitudes, and
phase constants. It is also possible to ‘reverse-engineer’ the
waves that have been superposed in order to obtain the final
resulting waveform. This is the rationale behind spectral
analysis, in which composite waveforms are decomposed
into their constituent waves. A Discrete Fourier Transform
(DFT) may be used for this purpose. However, the DFT is
subject to some weaknesses, discussed briefly below, which
makes it less than ideal for such an analysis.
31 After assigning
their SIMPLEX timescales to the two Indian Ocean sediment
cores, the Pacemaker authors used the Blackman–Tukey

Figure 4. Method used to obtain age estimates for the MIS stage boundaries within the V28-238
core. The MIS 8-7 boundary was identified at a depth of 430 cm within the V28-238 core. Hence, it
was assigned an age of 251 ka.

Figure 5. A complicated waveform may be constructed by adding together (superposing) waves
of different frequencies, amplitudes, and phase constants. All three component waves shown here
have an average value of zero.